staging: wilc1000: split add_key() to avoid line over 80 chars

Cleanup changes to fix 'line over 80 chars' issue found by checkpatch.pl
script by spliting the function. Also make use of kzalloc() instead
kmalloc().

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>